The present invention relates to an organopolysiloxane composition for fire-resistant foamed silicone rubber and a foamed silicone rubber body formed therefrom or, more particularly, to a foamable organopolysiloxane composition capable of giving a foamed silicone rubber body which can withstand a high-temperature flame in prolonged exposure retaining rubbery elasticity without consolidation or formation of cracks without losing usefulness as a filling material of throughgoing holes, for example, in buildings.
Several methods are known and practiced for the preparation of foamed bodies of a silicone rubber including the methods in which the foaming composition should be admixed with a blowing agent due to the absence of any foaming power in the organopolysiloxane composition per se and the methods in which the gaseous product produced in the condensation reaction for crosslink formation of the organopolysiloxane ingredient is utilized as the blowing agent to form a cellular foamed structure.
A typical method belonging to the former class is disclosed, for example, in Japanese Patent Publication No. 45-12675 according to which a foamed silicone rubber body is prepared by the decomposition gas of a heat-decomposable blowing agent admixed with an organopolysiloxane composition composed of a vinyl-containing organopolysiloxane having at least two silicon-bonded vinyl groups in a molecule and an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms in a molecule together with a platinum catalyst which promotes the addition reaction to form crosslinks between the vinyl-containing organopolysiloxane and the organohydrogenpolysiloxane. This method is not quite advantageous in the industrial production because the composition must be heated to effect the thermal decomposition of the blowing agent and expansion of the silicone rubber body is rather limited not to give a cellular foamed body of silicone rubber having a very low bulk density. On the other hand, a method belonging to the latter class is disclosed in Japanese Patent Publication No. 44-8875 according to which a hydroxy-containing organopolysiloxane having silicon-bonded hydroxy groups and an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms are reacted in the presence of an organic acid salt of heavy metals or a quaternary ammonium salt as the catalyst. A problem in this method is caused by the presence of such a catalytic compound of ionic nature in the composition which may be subject to depolymerization of the siloxane linkages when the composition or foamed silicone rubber body thereof is brought into contact with water or steam at high temperatures to lose the characteristic properties as a rubber.
The above mentioned disadvantages caused by the ionic compound contained in the composition as the catalyst can be solved when the catalyst for the condensation reaction of a hydroxy-containing organopolysiloxane and an organohydrogenpolysiloxane is replaced with a rhodium compound as is taught in Japanese Patent Publication No. 53-48224 or with a platinum compound as is taught in Japanese Patent Kokai No. 51-46352 and Japanese Patent Publications No. 52-42865 and No. 53-48225. The foamed silicone rubber bodies obtained by these improved methods are known to have an additional advantage of flame retardancy.
On the other hand, demand for such foamed silicone rubbers is rapidly growing in the field of building construction industries. Needless to say, a trend in the modern building technology is toward increasing numbers of multistoried high buildings as well as toward compliance with increasing requirements for safety design, especially, against fires. In this regard of safety against fires in buildings in general, it is indispensable or rather imperative that any opening in buildings must be provided with a fire-resistant, air-tight sealing means. Conventional sealing materials based on inorganic fibrous or putty-like substances are not quite satisfactory for such an application in respect of the resistance against fire and air-tightness. Accordingly, the above described foamed silicone rubbers formulated with a rhodium or platinum catalyst are sometimes used as a sealing material of buildings by virtue of their excellent resistance against fire and capacity of giving air-tightness to the seal. These improved foamed silicone rubbers are still not without problems as a fire-resistant sealing material since prolonged exposure of the foamed silicone rubber to flames causes decomposition and combustion of the silicone ingredients therein to convert the foamed body into a glassy clinker-like body of silicon dioxide or ashed body in which many cracks are necessarily formed through which the fire may further spread to increase the danger to human life and loss property by fire.
Accordingly, a further improvement has been proposed in Japanese Patent Kokai No. 57-141476 to increase the fire resistance of foamed silicone rubbers of this type by admixing the foaming organopolysiloxane composition with a phosphoric acid ester, hydrated inorganic compound capable of being endothermically dehydrated at a temperature of 60.degree. to 500.degree. C. and an inorganic fibrous material. A problem in this improved formulation is that the phosphoric acid ester may sometimes act as a catalyst poison against the platinum catalyst to cause incomplete curing of the silicone rubber. In addition, such a foamed rubber produces, when it is exposed to flames of speading fire, a large volume of smoke sometimes to cause fatal danger by the loss of view sight in escape from fire or in fireman works.